arXiv subjects

Pilar Coloma

Publications and source records attributed to Pilar Coloma.

At least 55 records · Page 3Linked to original sources

arXiv2016

The MOMENT to search for CP violation

In this letter, we analyze for the first time the physics reach in terms of sensitivity to leptonic CP violation of the proposed MuOn-decay MEdium baseline NeuTrino beam (MOMENT) experiment, a novel neutrino oscillation facility that would operate with neutrinos from muon decay. Apart from obtaining a sufficiently intense flux, the bottlenecks to the physics reach of this experiment will be achieving a high enough suppression of the atmospheric background and, particularly, attaining a sufficient level of charge identification. We thus present our results as a function of these two factors. As for the detector, we consider a very massive Gd-doped Water Cherenkov detector. We find that MOMENT will be competitive with other currently planned future oscillation experiments if a charge identification of at least 80 % can be achieved at the same time that the atmospheric background can be suppressed by at least a factor of ten. We also find a large synergy of MOMENT with the current generation of neutrino oscillation experiments, T2K and NOvA, which significantly enhances its final sensitivity.

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arXiv2016

Non-Standard Interactions in propagation at the Deep Underground Neutrino Experiment

We study the sensitivity of current and future long-baseline neutrino oscillation experiments to the effects of dimension six operators affecting neutrino propagation through Earth, commonly referred to as Non-Standard Interactions (NSI). All relevant parameters entering the oscillation probabilities (standard and non-standard) are considered at once, in order to take into account possible cancellations and degeneracies between them. We find that the Deep Underground Neutrino Experiment will significantly improve over current constraints for most NSI parameters. Most notably, it will be able to rule out the so-called LMA-dark solution, still compatible with current oscillation data, and will be sensitive to off-diagonal NSI parameters at the level of $\varepsilon \sim \mathcal{O}(0.05 - 0.5)$. We also identify two degeneracies among standard and non-standard parameters, which could be partially resolved by combining T2HK and DUNE data.

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arXiv2015

Right-handed neutrinos and the 2 TeV $W'$ boson

The CMS $e^+ e^- jj$ events of invariant mass near 2 TeV are consistent with a $W'$ boson decaying into an electron and a right-handed neutrino whose TeV-scale mass is of the Dirac type. We show that the Dirac partner of the right-handed electron-neutrino can be the right-handed tau-neutrino. A prediction of this model is that the sum of the $τ^+ e^+ jj$ and $τ^- e^- jj$ signal cross sections equals twice that for $e^+ e^- jj$. The Standard Model neutrinos acquire Majorana masses and mixings compatible with neutrino oscillation data.

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arXiv2015

Dark matter beams at LBNF

High-intensity neutrino beam facilities may produce a beam of light dark matter when protons strike the target. Searches for such a dark matter beam using its scattering in a nearby detector must overcome the large neutrino background. We characterize the spatial and energy distributions of the dark matter and neutrino beams, focusing on their differences to enhance the sensitivity to dark matter. We find that a dark matter beam produced by a $Z'$ boson in the GeV mass range is both broader and more energetic than the neutrino beam. The reach for dark matter is maximized for a detector sensitive to hard neutral-current scatterings, placed at a sizable angle off the neutrino beam axis. In the case of the Long-Baseline Neutrino Facility (LBNF), a detector placed at roughly 6 degrees off axis and at a distance of about 200 m from the target would be sensitive to $Z'$ couplings as low as 0.05. This search can proceed symbiotically with neutrino measurements. We also show that the MiniBooNE and MicroBooNE detectors, which are on Fermilab's Booster beamline, happen to be at an optimal angle from the NuMI beam and could perform searches with existing data. This illustrates potential synergies between LBNF and the short-baseline neutrino program if the detectors are positioned appropriately.

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arXiv2015

Missing energy and the measurement of the CP-violating phase in neutrino oscillations

In the next generation of long-baseline neutrino oscillation experiments, aiming to determine the charge-parity violating phase $δ_{CP}$ in the appearance channel, fine-grained time-projection chambers are expected to play an important role. In this Letter, we analyze an influence of realistic detector capabilities on the $δ_{CP}$ sensitivity for a setup similar to that of the Deep Underground Neutrino Experiment. We find that the effect of the missing energy, carried out by undetected particles, is sizable. Although the reconstructed neutrino energy can be corrected for the missing energy, the accuracy of such procedure has to exceed 20\%, to avoid a sizable bias in the extracted $δ_{CP}$ value.

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arXiv2015

Comparison of the calorimetric and kinematic methods of neutrino energy reconstruction in disappearance experiments

To be able to achieve their physics goals, future neutrino-oscillation experiments will need to reconstruct the neutrino energy with very high accuracy. In this work, we analyze how the energy reconstruction may be affected by realistic detection capabilities, such as energy resolutions, efficiencies, and thresholds. This allows us to estimate how well the detector performance needs to be determined a priori in order to avoid a sizable bias in the measurement of the relevant oscillation parameters. We compare the kinematic and calorimetric methods of energy reconstruction in the context of two muon-neutrino disappearance experiments operating in different energy regimes. For the calorimetric reconstruction method, we find that the detector performance has to be estimated with a ~10% accuracy to avoid a significant bias in the extracted oscillation parameters. On the other hand, in the case of kinematic energy reconstruction, we observe that the results exhibit less sensitivity to an overestimation of the detector capabilities.

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arXiv2015

Reassessing the sensitivity to leptonic CP violation

We address the validity of the usual procedure to determine the sensitivity of neutrino oscillation experiments to CP violation. An explicit calibration of the test statistic is performed through Monte Carlo simulations for several experimental setups. We find that significant deviations from a $χ^2$ distribution with one degree of freedom occur for experimental setups with low sensitivity to $δ$. In particular, when the allowed region to which $δ$ is constrained at a given confidence level is comparable to the whole allowed range, the cyclic nature of the variable manifests and the premises of Wilk's theorem are violated. This leads to values of the test statistic significantly lower than a $χ^2$ distribution at that confidence level. On the other hand, for facilities which can place better constraints on $δ$ the cyclic nature of the variable is hidden and, as the potential of the facility improves, the values of the test statistics first become slightly higher than and then approach asymptotically a $χ^2$ distribution. The role of sign degeneracies is also discussed.

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arXiv2014

Combining dark matter detectors and electron-capture sources to hunt for new physics in the neutrino sector

In this letter we point out the possibility to study new physics in the neutrino sector using dark matter detectors based on liquid xenon. These are characterized by very good spatial resolution and extremely low thresholds for electron recoil energies. When combined with a radioactive $ν_e$ source, both features in combination allow for a very competitive sensitivity to neutrino magnetic moments and sterile neutrino oscillations. We find that, for realistic values of detector size and source strength, the bound on the neutrino magnetic moment can be improved by an order of magnitude with respect to the present value. Regarding sterile neutrino searches, we find that most of the gallium anomaly could be explored at the 95% confidence level just using shape information.

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arXiv2014

Searching for sterile neutrinos at the ESS$ν$SB

The ESS$ν$SB project is a proposed neutrino oscillation experiment based on the European Spallation Source with the search for leptonic CP as its main aim. In this letter we show that a near detector at around 1 km distance from the beamline is not only very desirable for keeping the systematic errors affecting the CP search under control, but would also provide a significant sensitivity probe for sterile neutrino oscillations in the region of the parameter space favored by the long-standing LSND anomaly. We find that the effective mixing angle $θ_{μe}$ can be probed down to $\sin^2(2θ_{μe}) \simeq 2(8)\cdot 10^{-3}$ at $5σ$ assuming 15% bin-to-bin (un)correlated systematics.

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arXiv2014

Interplay between Appearance and Disappearance Channels for Precision Measurements of $θ_{23}$ and $δ$

We discuss how the CP violating phase $δ$ and the mixing angle $θ_{23}$ can be measured precisely in an environment where there are strong correlations between them. This is achieved by paying special attention to the mutual roles and the interplay between the appearance and the disappearance channels in long-baseline neutrino oscillation experiments. We analyze and clarify the general structure of the $θ_{23} - θ_{13} - δ$ degeneracy for both the appearance and disappearance channels in a more complete fashion than what has previously been discussed in the literature. A full understanding of this degeneracy is of vital importance if $θ_{23}$ is close to maximal mixing. The relative importance between the appearance and disappearance channels depends upon the particular setup and how close to maximal mixing Nature has chosen the value for $θ_{23}$. For facilities that operate with a narrow band beam or a wide band beam centered on the first oscillation extremum, the contribution of the disappearance channel depends critically on the systematic uncertainties assumed for this channel. Whereas for facilities that operate at energies above the first oscillation extremum or at the second oscillation extremum the appearance channels dominate. On the other hand, for $δ$ we find that the disappearance channel usually improves the sensitivity, modestly for facilities around the first oscillation extremum and more significantly for facilities operating at an energy above the first oscillation extremum, especially near $δ\sim \pm π/2$.

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arXiv2014

Neutrino-nucleus interaction models and their impact on oscillation analyses

In neutrino oscillation experiments, neutrino interactions at the detector are simulated using event generators which attempt to reflect our understanding of nuclear physics. We study the impact of different neutrino interactions and nuclear models on the determination of neutrino oscillation parameters. We use two independent neutrino event generators, GENIE and GiBUU, and apply them to a setup with a conventional neutrino beam aiming at a water Čerenkov detector, for which only the QE-like sample is selected. Subsequently, we perform a fit to the oscillation parameters in the $ν_μ$ disappearance channel.

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arXiv2014

Quantifying the sensitivity of oscillation experiments to the neutrino mass ordering

Determining the type of the neutrino mass ordering (normal versus inverted) is one of the most important open questions in neutrino physics. In this paper we clarify the statistical interpretation of sensitivity calculations for this measurement. We employ standard frequentist methods of hypothesis testing in order to precisely define terms like the median sensitivity of an experiment. We consider a test statistic $T$ which in a certain limit will be normal distributed. We show that the median sensitivity in this limit is very close to standard sensitivities based on $Δχ^2$ values from a data set without statistical fluctuations, such as widely used in the literature. Furthermore, we perform an explicit Monte Carlo simulation of the INO, JUNO, LBNE, NOvA, and PINGU experiments in order to verify the validity of the Gaussian limit, and provide a comparison of the expected sensitivities for those experiments.

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arXiv2013

Physics Performance of a Low-Luminosity Low Energy Neutrino Factory

We investigate the minimal performance, in terms of beam luminosity and detector size, of a neutrino factory to achieve a competitive physics reach for the determination of the mass hierarchy and the discovery of leptonic CP violation. We find that a low luminosity of $2\times 10^{20}$ useful muon decays per year and 5 GeV muon energy aimed at a 10 kton magnetized liquid argon detector placed at 1300 km from the source provides a good starting point. This result relies on $θ_{13}$ being large and assumes that the so-called platinum channel can be used effectively. We find that such a minimal facility would perform significantly better than phase I of the LBNE project and thus could constitute a reasonable step towards a full neutrino factory.

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arXiv2013

Gain fractions of future neutrino oscillation facilities over T2K and NOvA

We evaluate the probability of future neutrino oscillation facilities to discover leptonic CP violation and/or measure the neutrino mass hierarchy. We study how this probability is affected by positive or negative hints for these observables to be found at T2K and NOvA. We consider the following facilities: LBNE; T2HK; and the 10 GeV Neutrino Factory (NF10), and show how their discovery probabilities change with the running time of T2K and NOvA conditioned to their results. We find that, if after 15 years T2K and NOvA have not observed a 90% CL hint of CP violation, then LBNE and T2HK have less than a 10% chance of achieving a 5sigma discovery, whereas NF10 still has a ca 40% chance to do so. Conversely, if T2K and NOvA have an early 90% CL hint in 5 years from now, T2HK has a rather large chance to achieve a 5sigma CP violation discovery (75% or 55%, depending on whether the mass hierarchy is known or not). This is to be compared with the 90% (30%) probability that NF10 (LBNE) would have to observe the same signal at 5sigma. A hierarchy measurement at 5sigma is achievable at both LBNE and NF10 with more than 90% probability, irrespectively of the outcome of T2K and NOvA. We also find that if LBNE or a similar very long baseline super-beam is the only next generation facility to be built, then it is very useful to continue running T2K and NOvA (or at least T2K) beyond their original schedule in order to increase the CP violation discovery chances, given their complementarity.

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arXiv2012

Systematic uncertainties in long-baseline neutrino oscillations for large $θ_{13}$

We study the physics potential of future long-baseline neutrino oscillation experiments at large $θ_{13}$, focusing especially on systematic uncertainties. We discuss superbeams, \bbeams, and neutrino factories, and for the first time compare these experiments on an equal footing with respect to systematic errors. We explicitly simulate near detectors for all experiments, we use the same implementation of systematic uncertainties for all experiments, and we fully correlate the uncertainties among detectors, oscillation channels, and beam polarizations as appropriate. As our primary performance indicator, we use the achievable precision in the measurement of the CP violating phase $\deltacp$. We find that a neutrino factory is the only instrument that can measure $\deltacp$ with a precision similar to that of its quark sector counterpart. All neutrino beams operating at peak energies $\gtrsim 2$ GeV are quite robust with respect to systematic uncertainties, whereas especially \bbeams and \thk suffer from large cross section uncertainties in the quasi-elastic regime, combined with their inability to measure the appearance signal cross sections at the near detector. A noteworthy exception is the combination of a $γ=100$ \bbeam with an \spl-based superbeam, in which all relevant cross sections can be measured in a self-consistent way. This provides a performance, second only to the neutrino factory. For other superbeam experiments such as \lbno and the setups studied in the context of the \lbne reconfiguration effort, statistics turns out to be the bottleneck. In almost all cases, the near detector is not critical to control systematics since the combined fit of appearance and disappearance data already constrains the impact of systematics to be small provided that the three active flavor oscillation framework is valid.

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arXiv2012

A comparative study of long-baseline superbeams within LAGUNA for large $θ_{13}$

The Daya Bay and RENO experiments have recently observed a non-zero $θ_{13}$ at more than $5σ$ CL. This has important consequences for future neutrino oscillation experiments. We analyze these within the LAGUNA design study which considers seven possible locations for a European neutrino observatory for proton decay, neutrino, and astroparticle physics. The megaton-scale detector would be an ideal target for a CERN-based neutrino beam with baselines ranging from 130 km to 2300 km. We perform a detailed study to assess the physics reach of the three detector options - a 440 kton water Čerenkov, a 100 kton liquid argon and a 50 kton liquid scintillator detector - at each of the possible locations, taking into account the recent measurement of $θ_{13}$. We study the impact of the beam properties and detector performances on the sensitivity to CP-violation and the mass hierarchy. We find that a liquid argon or water Čerenkov detector can make a $3σ$ discovery of CP violation for $60%-70%$ of the parameter space for any of the baselines under consideration, although the results for the liquid argon detector placed at 130 km are slightly worse and only $40%-50%$ is achieved in this case. The performance of the liquid scintillator detector is affected by its level of neutral-current background at all baselines. A $3σ$ determination of the mass hierarchy is possible for all values of $δ$, for the values of $θ_{13}$ favoured at $3σ$ by Daya Bay and RENO, for almost all setups with $L\gtrsim 650$ km.

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arXiv2012

Physics reach of CERN-based SuperBeam neutrino oscillation experiments

We compare the physics potential of two representative options for a SuperBeam in Europe, studying the achievable precision at 1σwith which the CP violation phase (δ) could be measured, as well as the mass hierarchy and CP violation discovery potentials. The first setup corresponds to a high energy beam aiming from CERN to a 100 kt liquid argon detector placed at the Pyhäsalmi mine (2300 km), one of the LAGUNA candidate sites. The second setup corresponds to a much lower energy beam, aiming from CERN to a 500 kt water Čerenkov detector placed at the Gran Sasso underground laboratory (730 km). This second option is also studied for a baseline of 650 km, corresponding to the LAGUNA candidate sites of Umbria and the Canfranc underground laboratory. All results are presented also for scenarios with statistics lowered by factors of 2, 4, 8 and 16 to study the possible reductions of flux, detector mass or running time allowed by the large value of θ_{13} recently measured.

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arXiv2012

Precision on leptonic mixing parameters at future neutrino oscillation experiments

We perform a comparison of the different future neutrino oscillation experiments based on the achievable precision in the determination of the fundamental parameters theta_{13} and the CP phase, delta, assuming that theta_{13} is in the range indicated by the recent Daya Bay measurement. We study the non-trivial dependence of the error on delta on its true value. When matter effects are small, the largest error is found at the points where CP violation is maximal, and the smallest at the CP conserving points. The situation is different when matter effects are sizable. As a result of this effect, the comparison of the physics reach of different experiments on the basis of the CP discovery potential, as usually done, can be misleading. We have compared various proposed super-beam, beta-beam and neutrino factory setups on the basis of the relative precision of theta_{13} and the error on delta. Neutrino factories, both high-energy or low-energy, outperform alternative beam technologies. An ultimate precision on theta_{13} below 3% and an error on delta of < 7^{\circ} at 1 sigma (1 d.o.f.) can be obtained at a neutrino factory.

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